Have you noticed how advanced Gimp has been with the new version 2.10 ?
Now it work perfekt to open Fits 32 bit floating point images and process them. I have tried this many times earlier but it never worked very good. Now it's like a dream to work with.
I'm in the learning process how to use Gimp's capabilities. I have now got the opening process of three grey rgb images to work. It's of course not very complicated, but for me who never used Photoshop or something simular it was and I had hard to find a tutorial for the new version.
I have now made a tutorial for this first step how to start with Gimp and open 32 bits separated color images:
If you already working with Gimp, have you found something of special interest ?